The present invention is designed for use in a braking system wherein a brake shoe is caused to rub against a brake drum causing friction resulting in the braking action for a wheel.
The present invention is designed to enable the replacement of worn brake shoes with a new set of brake shoes such that the replacement brake shoe fits the drum just as uniformly as the worn brake shoe.
While the braking assembly described hereinafter is principally used in an automobile system, this is not deemed to be a limitation on the invention, rather, this is the best form of embodiment known to the Applicant.
A typical braking assembly comprises a stationary portion consisting of a backing plate and an anchor pin mounted on the backing plate. One end of each of a primary and secondary brake shoe are engageably positioned against an anchor pin and a hydraulic actuator mechanism. The other end of each brake shoe is connected to a brake adjustment mechanism. The movable portion of the braking assembly is the brake drum which rotates about the stationary braking subassembly. When the automobile is moving in the forward direction, the frontmost brake shoe (that toward the front of the automobile) is considered to be the primary brake shoe. The rear-most brake shoe (that toward the rear of the automobile) is considered to be the secondary brake shoe. The above relationship is based on the anchor pin being located at the top of the brake assembly.
When the brakes are applied while the car is moving in the forward direction, the primary shoe moves away from the anchor first and contacts the drum. The rotation of the drum causes the primary shoe to energize the secondary shoe. This contact between the primary shoe and the secondary shoe forces the secondary shoe against the anchor pin, limiting its movement. Since the movement of the secondary shoe is stopped by contact with the anchor pin, the secondary shoe is now forced against the drum causing friction to be generated between the drum and the secondary shoe causing the wheel to decelerate and eventually stop if the braking contact is not removed.
It is important to note that the secondary shoe fits snugly against the drum in its proper mode of operation. For the present invention to operate in its most efficient manner, it is assumed that in the original condition the secondary shoe is positioned equidistant from the drum over the length of the shoe. In other words, during manufacture the original shoe is placed in the subassembly and the manufacturing tolerances of the assembly is such that the braking surface of the shoe is positioned an equidistance from the surface of engagement of the drum. Since the original brake shoe is placed equidistant from the drum over the length of the shoe, then as the shoe wears during the braking process, it wears evenly over the entire surface area of the braking surface. During the braking action as described hereinabove, the secondary shoe is caused to bear against the drum surface and in this manner the secondary shoe is caused to fit intimately within the braking assembly. As mentioned hereinabove, the movement of the secondary shoe during forward movement is limited by the anchor pin. During the operation of the braking system and the wearing away of the braking material on the brake shoe, a very important relationship is established between the arc of the brake shoe as represented by the braking material and the engagement with the anchor pin.
When the brake shoes have been worn and it is time for their removal, a new set of brake shoes is obtained. The new brake shoes have been manufactured with a standardized arc of curvature for the braking material; however, there is no assurance that the arc of curvature of the replacement brake shoe will match the arc of curvature of the drum within the wheel assembly that the new shoes are to be positioned. If the arc of curvature of the replacement brake shoes do not closely match the arc of curvature of the brake drum, then the new brake shoes will wear unevenly; cause error in the brake adjustment mechanism of the brake assembly; cause failing of the brake system on a vehicle having more than one brake due to the unequal braking force generated in each of the wheels having a braking assembly. The purpose of the present invention is to eliminate these disadvantages and provide a mechanism and means whereby the replacement brake shoe is caused to match intimately the arc of curvature of the inner surface of the drum surface.
In the prior art, the replacement brake shoes are merely added into the braking assembly by removing the old brake shoes and substituting the new brake shoes without adjusting the arc of curvature of the replacement shoes or adjusting the engageable connection between the replacement brake shoes and the anchor pin.
In a second form of the prior art method of replacing brake shoes, the replacement brake shoes are placed on a grinding apparatus and sufficient braking material is removed from the new brake shoes so that the arc of curvature of the replacement brake shoes identically reproduces the arc of curvature of the old brake shoes. However, in this second mode of operation of the prior art replacement process, no effort is made in adjusting the relationship between the arc of curvature of the brake shoe and the engageable connection part of the brake shoe at the anchor pin. While the arc of curvature of the replacement brake shoe is caused to match the arc of curvature of the original brake shoe thus eliminating certain problems of the prior art, not all such problems are eliminated as will be described in greater detail hereinafter.